GEOTRACES: Inspired by GEOSECS to investigate trace elements and their isotopes in the ocean
Goldschmidt 2019 – Session 08m
Robert F. Anderson, Lamont-Doherty Earth Obs. Roger Francois, Univ. British Columbia Martin Frank, GEOMAR, Helmholtz Centre Ocean Res. Gideon Henderson, Univ. Oxford, Earth Sciences Catherine Jeandel, LEGOS, Toulouse Mukul Sharma, Dartmouth Coll., Earth Sciences
http://www.geotraces.org/ GEOTRACES: An international study of the marine biogeochemical cycles of trace elements and their isotopes
August 2019: • Cruises completed: 113 • Nations supporting cruises: 17 • Publications: > 1200 • Data shared publicly: http://www.geotraces.org/dp/idp2017
GEOTRACES: An international study of the marine biogeochemical cycles of trace elements and their isotopes
Inspired by GEOSECS . . .
. . . what do they have in common?
GEOTRACES: An international study of the marine biogeochemical cycles of trace elements and their isotopes
Inspired by GEOSECS . . .
. . . what do they have in common?
Both were created to address problems to large to be achieved without a large coordinated effort.
Large programs are required to address certain complex topics in oceanography
Selected historical examples
• Overturning circulation of the ocean
• Ocean-atmosphere partitioning of carbon (both natural and anthropogenic)
• Global biogeochemical cycles
Birth of GEOSECS – To quantify the rate of ocean overturning circulation
Henry Stommel
Motivated GEOSECS by identifying a problem too large to solve without a large program
Photo from chapter by Walter Munk in 50 years of Ocean Discovery Atlantic early 14C data helped constrain rate of overturning circulation (Broecker et al., JGR 1960)
North South
West
East Birth of GEOSECS
“Ed Goldberg (Scripps Institution of Oceanography) and I were attending some sort of meeting at WHOI during the late 1960s. Hank came to us and said that radiocarbon measurements in the sea were of great importance. He went on to gently chastise us (the geochem community) for doing only scattered stations.
What is needed, he said, is a line of stations extending the length of the Atlantic.
Gee, we said, that would cost a million dollars, a sum greater than the entire NSF annual budget for ocean chemistry.
Hank replied, “Well it would be worth more than a million.”
Quote from Wally Broecker repeated in John Farrington’s chapter in 50 Years of Ocean Discovery - Confirmed by personal communication with Wally Harmon Craig Karl Turekian
Wally Broecker
Arnold Joe Reed Bainbridge
GEOSECS 1972-1978 First global survey of ocean chemistry 28 Investigators, 14 institutions, $24M Slide Courtesy Chris Measures Derek Spencer John Edmond GEOSECS Success – Ocean Ventilation Time Scales
Derek Spencer Broecker & Wally Broecker Peng 1982 Arnold Bainbridge GEOSECS Success: First assessment of the
ocean’s uptake of anthropogenic CO2 GEOSECS Success – Foundation for Future Programs
• TTO - Transient Tracers in the Ocean
• WOCE - World Ocean Circulation Experiment
• JGOFS - Joint Global Ocean Flux Study (JGOFS)
• CLIVAR Repeat Hydrography (GO-SHIP)
• GEOTRACES
• and more
Where’s Wally? Trace elements and their isotopes
GEOSECS + 20 to 30 years
History repeats itself (there is a lesson here) Two decades of work on iron was insufficient to characterize its biogeochemical cycle
Stations as of 2003 with dissolved Fe data to depths > 2000 m - Compiled by Payal Parek Reproduced from Anderson et al., 2014 Two decades of work on iron was insufficient to characterize its biogeochemical cycle
Situation ca. 2000 was even worse for other trace elements and isotopes. A new strategy was needed. GEOTRACES: Timeline – Selected milestones Lesson: Be patient
2000 Initial discussions and planning for “GEOSECS-II” 2001 Special session & Town Hall to assess interest 2003 International planning workshop – define goals 2004 SCOR accepts oversight 2005 Initiate data management 2006 Complete science plan 2006 Initiate intercalibration 2007 Pilot studies – International Polar Year 2010 Launch main field program 2014 Release of first data product 2015 Launch synthesis initiative 2017 Second data product 2019 Mid-life review GEOTRACES Discoveries – Prominent Fe sources from ridges and margins
Fe residence time is so short that its distribution is dominated by its sources
Clear source signatures: - Dust - Sediment - Hydrothermal - Rivers
Source: www.eGEOTRACES.org
GEOTRACES Discoveries – Prominent Fe sources from ridges and margins
Fe residence time is so short that its distribution is dominated by its sources
Clear source signatures: - Dust - Sediment - Hydrothermal - Margins
Source: www.eGEOTRACES.org
GEOTRACES Discoveries – Dual behavior of Co
• Dominant source in shelf & upper slope sediments • Cycles with P in the upper water column (nutrient)
(A) • Scavenged by Mn in deep water • Residence time • ~ 7 yrs in upper 250 m • ~1000 yrs in deep sea • Most Co in pelagic sediments derived from (B) upper ocean
Top: Atlantic zonal Co section (Noble et al., 2017) Bottom: Pacific zonal Co section (Hawco et al., 2016, 2018)
Figure 5. Concentrations of dissolved Co measured along zonal GEOTRACES sections (A) between North America and North Africa (Noble et al 2017) and (B) between Peru and Tahiti (Hawco et al 2016). Dissolved oxygen concentrations are overlain as contours. Elevated Co concentrations are seen within low-oxygen water on the eastern boundary of each section, thought to reflect mobilization of Co bound to Mn oxides that are reduced in organic-rich upper margin sediments, and within Labrador Seawater roughly between 1000 m and 2000 m depth on the western boundary in (B). Data are available in the GEOTRACES Intermediate Data Product IDP2017 (Schlitzer et al 2018). Figure produced using Ocean Data View < http://odv.awi.de>.
Tracers in the Sea – 1982 Wally set the standard for synthesis of findings
Aboard the Knorr
In his Lamont Office
Photos from Patty Catanzaro GEOTRACES Synthesis Themes/Goals: Identify processes and quantify fluxes
- Inputs and outputs at the interfaces of the ocean - Internal cycling within the ocean Uncertainty about iron emphasizes need for better fluxes and residence times 1000
100
10
Iron Residence Time (years) Time Iron Residence 1 1 10 100 Global Iron Supply (Gmol/yr)
- Output from 13 global ocean biogeochemical models - Two orders of magnitude uncertainty (range among models) Tagliabue et al., 2016 GEOTRACES Synthesis: Quantifying fluxes and comparing different approaches
Solid-phase 230Th mass balance 25 Model Core top
/yr) 20 2 230Th-norm susp. part. flux 15 Sinking rate suspended particles
10 Dust flux (g/m Comparison of 8 methods to 5 estimate dust flux. Phil. Trans. Roy. Soc. A, 2016 0 -50 -40 -30 -20 Longitude GEOTRACES Synthesis: Combining trace elements & radionuclides to estimate residence times
Full water column replacement times (red bars): Shorter than previous estimates for Fe and Mn Hayes et al., GBC, 2018 GEOTRACES Synthesis: Current and future work
• Many studies quantifying fluxes and residence times.
• Micronutrient speciation and bioavailability
• Identifying new processes not yet in models
Following the spirit of GEOSECS synthesis led by Wally Broecker GEOSECS Original Panel Members
Wallace S. Broecker Lamont-Doherty Geological Observatory Harmon Craig Scripps Institution of Oceanography H. Göte 0stlund University of Miami P. Kilho Park Oregon State University Joseph L. Reid Scripps Institution of Oceanography Derek W. Spencer Woods Hole Oceanographic Institution Henry M. Stommel Massachusetts Institute of Technology Taro Takahashi California Institute of Technology* (LDEO) Karl K. Turekian Yale University Herbert L. Volchok Atomic Energy Commission
From Turekian, 1970, JGR Intro to special issue on GEOSECS test station